Bone is a living tissue and plays a structural role in the body. Bone consists of repeating Harvesian systems (concentric layers of lamellae deposited around a central canal containing blood vessels and nerves). The central canal is also known as the medullary cavity and is filled with bone marrow. Within the shaft of a long bone, many of these Harvesian systems are bundled together in parallel, forming a kind of bone called compact bone, which is optimized to handle compressive and bending forces. In some bones, such as the metacarpals, the bones themselves are hollow and contain little, if any, marrow. Near the ends of the bones, where the stresses become more complex, the Harvesian systems splay out and branch to form a meshwork of cancellous or spongy bone. Compact bone and cancellous bone differ in density, or how tightly the tissue is packed together.
The structure of bone is similar to reinforced concrete that is used to make a building or a bridge. When the building or bridge is first assembled, an initial frame that contains long steel rods is put in place. Cement is then poured around these steel rods. The rods and the cement form a tight union, producing a structure that is strong and resilient enough to withstand some rocking motion while maintaining strength. Without the steel rods, the cement would be brittle and fracture with only minor movement. Without the cement, the steel rods would have inadequate support and would bend. The same organization is true of bone. The steel rods that support the building are collagen rods in bone. The cement that surrounds and supports the rods is formed by minerals (including calcium and phosphorus) from the blood that crystallize and surround the collagen rods. These minerals give the bones strength while the collagen rods provide resiliency.
Genetic or developmental irregularities, trauma, chronic stress, tumors, and disease can result in pathologies of bones. Some bone diseases that weaken the bones include, but are not limited to, osteoporosis, achondroplasia, bone cancer, fibrodysplasia ossificans progressiva, fibrous dysplasia, legg calve perthes disease, myeloma, osteogenesis imperfecta, osteomyelitis, osteopenia, osteoporosis, Paget's disease, and scoliosis. Weakened bones are more susceptible to fracture, and treatment to prevent bone fractures becomes important. Severe fractures, such as those that are open, multiple, or to the hip or back, are treated in a hospital. Surgery may be necessary when a fracture is open, severe, or has resulted in severe injury to the surrounding tissues. Severe fractures may require internal devices, such as screws, rods, or plates, to hold the bone in place or replace lost bone during the healing process.
In many cases where the bone has fractured, a bone cement mixture, or a bone void filler, is added into the bone to repair and strengthen the bone. Prior art bone cement mixtures are typically two part (powder and liquid), require a catalyst, and are exothermic. Injection devices similar to a household caulking gun are used to inject bone cement into bone. A typical bone cement injection device has a pistol-shaped body, which supports a cartridge containing bone cement where the injection device is usually a high pressure delivery source. More specifically, a trigger actuates a spring-loaded or screw ram, which forces a volume of bone cement in a viscous condition through a suitable nozzle and into the interior of a bone targeted for treatment. The amount of bone cement mixture injected is a function of the amount of space within the bone structure and the ability to reach the open areas in the bone. In some cases the presence of bone marrow restricts the amount of bone cement mixture that can be used, therefore before a bone cement mixture can be added into the bone for repair, the bone marrow must be removed from the area.
In thermal characterization tests of polymethylmethacrylate (PMMA) bone cement performed according to the ASTM Standard Specification for Acrylic Bone Cement, time and temperature profiles of bone cement were observed to be sensitive to the thickness of the cement patty and the mold material. Due to the heat transfer from the cement to the surrounding mold, such tests might underestimate the exothermic temperature of bone cement. That is, the mold material and geometry may influence the values of the parameters measured.
Bone cements may be difficult to work with and cause complications. Leakage of bone cements can result in soft tissue damage as well as nerve root pain and compression. Other complications associated with the use of bone cements for vertebroplasty and kyphoplasty procedures may include pulmonary embolism, respiratory and cardiac failure, abdominal intrusions, ileus, and death.
Prior art techniques for adding a bone cement mixture to repair or strengthen bone are described in U.S. Pat. No. 4,969,888 entitled “Surgical Protocol for Fixation of Osteoporotic Bone Using Inflatable Device,” U.S. Pat. No. 5,108,404 entitled “Surgical Protocol for Fixation of Osteoporotic Bone Using Inflatable Device,” U.S. Pat. No. 5,824,087 entitled “Bone Regeneration,” U.S. Pat. No. 6,241,734 entitled “Systems and Methods for Placing Materials Into Bone,” U.S. Pat. No. 6,395,007 entitled “Apparatus and Method for Fixation of Osteoporotic Bone,” U.S. Pat. No. 6,425,923 entitled “Contourable Polymer Filled Implant,” U.S. Pat. No. 6,887,246 entitled “Apparatus and Method for Fixation of Osteoporotic Bone,” U.S. Pat. No. 6,875,212 entitled “Cureable media for implantable medical device,” U.S. Pat. No. 6,964,667 entitled “Formed in place fixation system with thermal acceleration,” U.S. Publication No. 2004/0225296 entitled “Devices and methods using an expandable body with internal restraint for compressing cancellous bone,” and U.S. Publication No. 2005/0142315 entitled “Liquid perfluoropolymers and medical applications incorporating same.”
The prior art injection devices are typically invasive and have difficulty quickly terminating the flow of cement should the cavity fill before the spring-actuated load cycle is completed. Conventional cement injection devices also have difficulty adjusting or controlling the injection volume or injection rate in real time in reaction to cancellous bone volume and density conditions encountered inside the bone.
Thus, there is a need in the art for apparatuses and methods for delivering reinforcing materials into a bone using minimally invasive techniques, with ease of use, greater rate and volume control and a faster response time.